1. Field of the Invention
The present invention relates to a method for forming a silicide film having a uniform surface, and more particularly to a method for forming the silicide film used in semiconductor such that a conducting layer used in semiconductor, for example a conducting layer for the gate electrode of MOSFET, is formed sequentially with a doped polysilicon (or doped amorphous silicon and an undoped polysilicon (or undoped amorphous silicon). A silicide film is then formed in the undoped polysilicon by heat treatment in a furnace of a metal layer formed on the undoped polysilicon.
2. Information Disclosure Statement
In general, the polysilicon used as a conducting layer and has a sheet resistance of, for example, about 50 ohm/.quadrature.. As the integrity of the memory device increases, the line width of the conducting layer decreases, thereby increasing the line resistance of the conducting layer. Therefore RC delay time is increased if the line resistance of the conducting layer is increased.
Therefore, if a silicide film is formed on the conducting layer, the resistance value of the silicide film can be reduced to less than 1/10 compared with the resistance value of the polysilicon conducting layer without the silicide film, thereby decreasing the RC delay time and enhancing the current transfer capability of the device.
In general, an embodiment for forming a silicide film used in the semiconductor device in the prior art has been proposed such that an impurity doped polysilicon, such as a conducting layer, is formed on the substrate. A metal layer is then deposited on the polysilicon and a silicide film is then formed by heat treatment of the metal layer deposited on the polysilicon. However, according to the above mentioned prior art process the surface of the resultant silicide film is rough and does not have a uniform thickness. That is, when the silicide film is selectively formed on the gate electrode, source electrode and drain electrode in the case of the MOSFET, if the concentration of which N type impurity (phosphorus or arsenic) contained in the polysilicon and which thermally reacts with the metal layer, is above 10 to the 20th power (Atoms/cubic cm), the speed of reaction therebetween becomes too slow. Therefore in order to form the desired thickness of the silicide film either more thermal processing or more thermal processing time is required. However, if rapid thermal annealing equipment is utilized in order to apply longer thermal processing time the throughput in the process is reduced; and if the higher thermal processing is utilized, the surface of the silicide film becomes too rough. Also, if the concentration of phosphorus and arsenic increases, a problem occurs in that the interface between the resultant silicide film and the surface of the silicon layer becomes significantly rough.
Accordingly in order to solve the problem mentioned above, attempts had been made to form a uniform surface of the silicide film by lowering the impurity concentration of the phosphorus or the arsenic to form the N+ region at source region and drain region of the MOSFET, and after the silicide film is preformed, a uniform surface thereof is formed by forming the N+ region by ion implantation at the source region and drain region of the MOSFET. However, the concentration of the polysilicon which is used as the gate electrode of the MOSFET cannot be lowered because the work function of the polysilicon should be stably maintained, and the implantation of the impurity is impossible if the silicide film has been formed over the polysilicon layer.
Accordingly, it is an object of the present invention to solve the problems presented in the prior art and to provide a method for forming a uniform silicide film on the conducting layer used in the semiconductor device.